The present invention relates to a process for detecting the limit level of liquids and bulk materials in containers and pipelines, in which the change of the oscillation behavior of a sensor which is excited to oscillation is detected electronically and used to trigger a switch command. The invention also relates to an apparatus suitable for the carrying out of the process.
Containers or tanks are used in practically all applications of pipeline systems. Frequently, when a minimum level therein is reached, a switch signal must be given off which, for instance, controls a pump for the filling of a container. If the upper level of filling is reached by the end of a given period of time, then the pump must be turned off by a second switch signal. It is also conceivable that a pump to convey a fluid out of a tank until a minimum level has been reached. The pump must then be turned off in order to avoid having it operate dry. In may industrial processes, it is also necessary to know whether a pipeline is full or empty. For example, in the case of centrifugal pumps running dry is generally to be avoided so that a pump should be turned on only when the pipe on the intake side is full.
For the detection of the limit level, so-called vibration limit switches are known, for instance from Federal Republic of Germany 42 03 967 C2. The vibratory part used as sensor consists of a vibratory fork, the vibration behavior of which changes as the sensor is covered by the material being introduced. This change in oscillation is detected by an integrated measurement electronic system and a switch command is given. Limit switches which are based on the oscillating-fork principle are strong, accurate, free of adjustment, and require little maintenance. Made of metal, they are, however, unsuitable, or scarcely suitable, for many fluids or for highly pure uses.
In view of this prior art, it is the principle object of the present invention to provide a method, as well as an apparatus, of the aforementioned type which, in addition to said advantages of the processes and apparatus based on the vibration principle, have a broader field of use with respect to liquids.